For transmitting the input power and adapting the engine torque to the traction a vehicle needs, there are practically only used today multi-stage gearwheel transmissions.
The transmission control can be considerably simplified by means of a synchronizing device. In the synchronization, the speed adaptation of the transmission elements to be interconnected is carried out automatically or controlled in order to prevent the double clutch when upshifting or the double clutch with intermediate blipping of the throttle when downshifting. The security in traveling is clearly improved, since even in critical traveling situations, it is possible to change gears quickly, reliably and also noiselessly, the driver's right foot, for example, can remain on the brake while downshifting when traveling downhill.
A synchronizer device has to perform the following tasks:
a speed adaptation of two transmission elements and parts connected therewith rotating at different speeds so that they can be form-fittingly interconnected without grating noise; PA1 locking of the form-fitting connection until synchronous speed of the transmission elements to be connected in order to prevent grating noises and damages of the form-fitting gearshift elements; PA1 release of the locking at the moment of the synchronous speed; PA1 speed adaptation within the shortest time and with as low as possible gearshift forces; PA1 security of operation even under unfavorable circumstances such as when the transmission oil is cold, viscous or under extremely quick breaking of the gears. PA1 connections that can be closed and dissolved as often as desired of two parts rotating on a common axis, PA1 transmission of energy to, or removal of energy from, a rotating part (acceleration, braking), PA1 adjustment of speed difference between two parts rotating on a common axis to a value equal to or approximate to zero.
The synchronized vehicle transmissions existing today, mostly use synchronizer devices for each individual gear.
The locking synchronization with conical adapter has become widespread. In this system are used conical friction cones for the force-locking speed adaptation of the transmission elements to be connected. This kind of synchronization is used both in passenger cars and in commercial vehicles.
Gearwheel and accessory clutch bodies are firmly interconnected. The clutch body has one friction cone and carries outside the selector teeth. The synchronizer sleeve is non-rotatably, but axially movably situated upon the synchronizer body, which sits firmly on the main shaft of the transmission. Each recess of the synchronizing body has a compression spring, a ball pin and a pressure piece. In the central position of the synchronizer sleeve, the springs press the ball pins through a bore in the pressure piece into a V-shaped recess of the synchronizer sleeve. Between the clutch and synchronizing bodies is situated the synchronizing ring which can perform relative to the synchronizing body a rotary motion limited by stops. The synchronizing ring likewise has a friction cone and carries on the external diameter the so-called locking teeth.
In idle, the synchronizer sleeve is in an axial central position. The gearwheels can freely rotate upon the transmission main shaft. Due to axial movement of the synchronizer sleeve, the synchronizing ring is pressed by means of ball pins and pressure pieces against the friction cone of the clutch body. Due to the speed difference of the parts to be coupled, the synchronizing ring is turned around the synchronizer sleeve as far as the stop. In this position, the locking teeth prevent the further axial movement of the synchronizer sleeve.
The axial gearshift force exerted on the synchronizer sleeve is transmitted, via the beveled teeth, to the friction cones of the synchronizing ring and the clutch body, reinforced on the friction cone, transformed to a torque and thus effects a reduction of the speed difference which becomes quicker as the gearshift force becomes stronger and thus synchronizing the torque. The chamfering angle of the locking teeth is designed so that the torque produced on the synchronizing ring, by means of the gearshift force of the synchronizer sleeve, is less than the friction torque acting opposite thereto on the cone. After achieving the synchronous speed, the synchronizing ring is turned back by the restraining gearshift pressure of the synchronizer sleeve until the teeth of the synchronizer sleeve stand before the tooth gaps of the synchronizing ring and a passage through the locking teeth for noiseless engagement of the gear is possible.
Such a locking synchronizing device has been disclosed, for example, in "ZF-B-Sperrsynchronisierung"/publication 42290/R 2964-367 of March 1967.
The locking synchronizing device described in said publication is designed so that when the clutch body is pressed on the friction cone, the synchronizing ring, provided with outer teeth, performs a rotary motion limited by the stops on the synchronizing body. The consequence of said rotation is that the beveled front faces of the teeth of the synchronizing ring press against the synchronizer sleeve and thus prevent further movement of the sleeve. Only when the cone friction surfaces have contributed to the synchronous speed of the parts to be coupled does the restraining pressure of the synchronizer sleeve effect a turndown of the synchronizing ring. The lock is thus released and the synchronizer sleeve is pushed into the teeth of the clutch body.
During idling, the synchronizer sleeve is in an axial central position. The detent pins are pressed by springs into detents of the synchronizer sleeve. The idler wheels can freely rotate upon their shafts. The speed difference between synchronizing ring and clutch body and the drag torque between their friction faces cause the synchronizing ring to abut on the rotary stop of the synchronizing body. The beveled tooth faces of the synchronizer sleeve and synchronizing ring are opposite each other.
In the locking position, the synchronizer sleeve has first moved the synchronizing ring against the clutch body by the detent pins and pressure pieces. The tooth faces have thus assumed the further guidance of the gearshift force from the synchronizer sleeve directly to the synchronizing ring. As long as a speed difference exists between the synchronizing ring and clutch body, the friction torque on the cone friction faces of synchronizing ring and clutch body is stronger than the restoring torque through the beveled tooth faces. The synchronizer sleeve is, therefore, locked against cutting into the clutch body.
Only when the speed difference between synchronizing ring and clutch body has been adjusted and the friction torque thus removed does the synchronizer sleeve move the synchronizing ring back to the position of "tooth upon tooth gaps". Over the locking teeth of the synchronizer ring, the synchronizer sleeve is then inserted into the teeth, likewise beveled on the front side, of the clutch body.
This known synchronizing device needs considerable improvement as to operation and cost of production. Improvement is also needed in the strong gearshift force required in low gear steps and the unsatisfactory shifting feel which makes itself noticeable in a certain jam during the gearshift operation, an unsatisfactory unlocking inhibition and force peaks when meshing. Force peaks occur after synchronization, generally designated as "2nd point", which are caused by the buildup of a differential speed in the free flight phase or an impact incident when the teeth impinge upon each other combined with a great inertia moment. They act as accelerations on the gear-shift lever. The synchronizing device of known design also requires large space. Existing demand for reductions, low weight and high complexity are not satisfied by it.
The customary synchronizing devices have at their disposal the three basic functions of synchronization
Examining a gearshift operation of the known synchronizing device with regard to the negative influences on the shifting feel, the phases after achieving the synchronous speed are especially conspicuous.
The locking position can only be canceled by exerting force on the gearshift lever turning the free rotating masses by one half tooth pitch of the coupling teeth. The synchronizing ring is designed to lock and secure by the selection of tapering angle and geometry of the locking teeth. Against the unlocking torque abutting on the locking teeth, an equally strong reaction torque of the inert rotary mass acts via the friction cone, thus preventing a separate rotation of the ring relative to the free rotary masses. It is only in the "free flight phase" between unlocking and impinging of the coupling teeth that the synchronizing ring should have released itself from the friction cone. An adherence during meshing of the coupling teeth would cause a breaking up of the ring and therewith additional need of force.
Disadvantages result during high drag torques on the free rotary masses of the transmission due to the lack of torque transmission in the "free flight phase". During the short interval of time without torque transmission between the rotary masses to be coupled, a speed difference again builds up. Accordingly, hard percussive and therewith rejection forces make themselves unpleasantly noticeable when the coupling teeth impinge on each other in the gearshift lever. This problem becomes more acute in the synchronizing devices used today due to the requirement determined by construction of keeping at least the gradient angles on the locking and meshing teeth at equal values.
In synchronizing devices with friction discs, the conical friction members are replaced by a number of discs which rub against each other during the speed adaptation. Here discs axially adjacent to each other in sequence are connected either on one side with the synchronizing ring or the transmission shaft, or on the other side, with the clutch body or the gearwheel itself. Such a synchronization device which, for example, can be equipped with a reinforcing device of the synchronization force, has been disclosed in DE 32 08 945.
From U.S. Pat. No. 1,777,012 is also known a synchronizing device having friction discs. An axially movable element for connecting a transmission shaft with a gearwheel consists of an outer disc carrier with teeth and an inner disc carrier with coupling teeth. Between both annular disc carriers are situated friction discs which are each axially consecutively connected with both disc carriers. Each disc carrier supports a set of friction discs. The friction discs are adjacent to each other without being pressed together by a predetermined force. Only by the gearshift force introduced by the driver, which at first axially moves only the first disc carrier with its set of friction discs, are the two sets of friction discs pressed against each other. The inner disc carrier has on its axially opposite ends clutch dogs which engage in the teeth of the gearwheel to be shifted. The inner disc carrier likewise has internal teeth with which it can be axially moved on the shaft between the teeth. The outer disc carrier has gripping teeth which project axially farther than the coupling teeth on the inner disc carrier so that the outer disc carrier reaches the gearwheel sooner. The sets of friction discs are situated between the two disc carriers in a manner such that on one side the outer disc abuts on stops and the outer disc on the other side is secured by stop rings. In the disengaged state, the inner disc carrier lies with an annular spring in an area without teeth upon the transmission shaft. If the disc carriers are axially moved away from the neutral position by a gearshift fork, this movement transmits itself from the outer disc carrier in which the gearshift fork meshes, via the disc sets, to the inner disc carrier. The inner disc carrier can first move along unhindered, but then the annular spring runs up on facets of the teeth to the transmission shaft where it generates a friction which prevents the axial movement. The friction between the disc sets is thereby reinforced and the adaptation of speed is achieved.
The disadvantage here is that to produce the synchronous moment, the adjacent gearshift force is required. Without the adjacent gearshift force and the friction produced by the axial movement between annular spring and dogs, no synchronous moment is generated between the friction discs. Neither the gripping teeth nor the coupling teeth are spring mounted here.